Conventionally, studies have been made on the technology relating to such the display device for the observer to make a sense that a video or picture is displayed in a space.
For example, in the following Patent Document 1 is disclosed a technology for forming an actual image (i.e., the video), easily, by guiding light rays information of a target laying on an opposite side to the observer through orthogonal flat reflectors, within a space defined between the observer and the orthogonal flat reflectors.
Also, in the following Patent Document 2 is disclosed a technology for enabling a freely settable viewpoint to observe the actual image (i.e., the video) by means of a mirror, with forming that actual image (i.e., the video) at a position being symmetric thereto, by transmitting the light while refracting it therein with using an optical system, in which orthogonal two mirror surface elements are formed on a plane by a plural number thereof, and also the mirror therein.